In providing cardiac pacing, there is a preference to promote intrinsic conduction and intrinsic depolarization of the ventricles and to reduce or minimize ventricular pacing. Various protocols have been provided to promote intrinsic conduction with varying degrees of success. For example, in some modes a programmed AV (atrial-ventricular) delay is extended and if underlying conduction is present, the sensed ventricular event will inhibit a subsequent ventricular pace. While useful, such AV extensions are limited in that the maximum intervals available must remain consistent with the capabilities of traditional pacing modalities. That is, such an AV interval may be defined within a DDD or DDDR mode, for example. For any given cardiac cycle, a ventricular pace will be delivered at the end of the AV delay absent sensed ventricular activity. Therefore, there is a maximum AV delay, beyond which a ventricular pace may not be safely delivered in a given cardiac cycle.
According the protocols of the present invention and as defined in greater detail in the above incorporated applications, modes are provided that permit an entire cardiac cycle to pass without ventricular pacing, even in the absence of a sensed ventricular event. This provides the maximum opportunity during a given cardiac cycle for intrinsic conduction to occur. Such protocols may be referred to collectively as “Managed Ventricular Pacing™” (MVP™) or a “ventricular pacing protocol” (VPP).
In practice, a given patient may perform quite well with a given VPP that provides no ventricular pacing; that is, effectively acting in an AAIR, AAI, ADI, or ADIR mode so long as intrinsic conduction is either always present or lacking so infrequently as to be tolerated by the VPP. Other patients, for example those with complete heart block, may be pacemaker dependant and require constant ventricular pacing. In such instances, the VPP does not have any opportunity to reduce ventricular pacing, as that pacing is critical for survival. Finally, there are patients who fluctuate between the two extremes. These patients will sometimes require ventricular pacing and at other time will exhibit intrinsic conduction either at normal or prolonged intervals.
With the patients who fluctuate, the VPP will operate in an atrial based pacing mode when permissible and operate in a dual chamber pacing mode when ventricular pacing is required. It should be appreciated that the present description is provided as an overview and is not meant to be limiting; that is, in some instances the VPP will mode switch from one mode to another whereas in other instances the VPP includes a single mode that effectuates both the atrial based and dual chamber based functionality. Thus, for purposes of description an indication of an atrial based or dual chamber based mode (with reference to a VPP) is indicative of the functionality imparted and includes either an actual mode status/switch or the functional status of a VPP using a single mode inclusive of both aspects. Furthermore, atrial based pacing mode simply means that ventricular pacing is generally not provided (for a given cycle) and a dual chamber mode means that ventricular pacing is available. Thus, these distinctions, as used herein do not preclude triple chamber pacing, four chamber pacing, or other multi-site pacing arrangements.
As indicated, various patients will fluctuate between requiring and not requiring ventricular pacing. As such, a change to a dual chamber based pacing mode is generally not expected to be permanent. That is, the device will periodically perform conduction checks to determine if intrinsic conduction is present and therefore facilitate a return to an atrial based pacing mode.